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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

In Situ EXAFS Study of Mo–P Bond Dynamics in Molybdenum Phosphide during CO 2 Reduction and Hydrogen Evolution

Transition Metal Phosphides (TMPs) are widely studied as catalysts in reactions like hydrogen evolution, oxygen reduction, and hydrodesulfurization. TMPs have demonstrated remarkable efficiency in accelerating reactions by providing active sites for adsorption and facilitating the transformation of reaction intermediates, a feature that has increased the interest of TMPs in the electrochemical carbon dioxide reduction reaction (eCO 2 RR). Despite their growing use, the potential-dependent structural behavior of TMPs under operating electrochemical conditions remains insufficiently understood. This work investigates the dynamics of the Mo−P bond during eCO 2 RR and hydrogen evolution reaction (HER) using in situ extended X-ray absorption spectroscopy (EXAFS) studies at the Mo−K edge. Structural characterization of the synthesized MoP nanoparticles was performed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results of the overall electrochemical activity of MoP are presented through linear sweep voltammetry (LSV) experiments in the potential range of 0 to −1.5 V versus Ag/AgCl and chronoamperometry (CA). Liquid products were analyzed by 1 H NMR spectroscopy. The synthesized catalyst showed increasing activity with the highest Faradaic efficiency of 11.75% for C 2+ products at −1.3 V vs Ag/AgCl. In situ EXAFS revealed a change in the average Mo−P bond distance during eCO 2 RR, whereas no such change was observed during the hydrogen evolution reaction (HER). This finding suggests that phosphorus, particularly through modulation of the Mo−P bond length, plays an important role in the eCO 2 RR and demonstrates how in situ EXAFS can track local structural perturbations in MoP catalysts during electrochemical operation, providing complementary structural insight that correlates with electrochemical behavior.

Catalysts↗
DOE OSTI2025

Direct Synthesis of Polyester from Biomass Derived 1,6-hexanediol using a Copper-Ceria Catalyst

Biomass derived polyesters are gaining attention due to their increased mechanical and thermal properties, and also because of their biodegradability. These polyesters are typically synthesized from polycondensation reactions between diols with dicarboxylic acids using catalysts. Other methods such as alcoholysis and acidolysis of low molecular weight esters and alcoholysis of acyl chlorides are also well known. Direct conversion of diol to ester without using dicarboxylic acid is not well known, and to our knowledge has not been reported over a solid catalyst. In this study, we report a direct synthesis of polyester from 1,6-hexanediol using a copper-ceria catalyst without using a dicarboxylic acid monomer. The copper-ceria catalysts were synthesized by incipient wetness impregnation method and characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET), and infrared spectroscopy (IR). Our initial studies show that 1,6-hexanediol can be converted to corresponding polyester at higher temperatures under atmospheric pressures of CO2 or N2. The reaction products were analyzed using nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), and IR spectroscopy.

Biomass derived diols↗
DOE OSTI2022

The Structure of Liquid and Glassy Carbamazepine

To enhance the solubility of orally administered pharmaceuticals, liquid capsules or amorphous tablets are often preferred over crystalline drug products. However, little is known regarding the variation in bonding mechanisms between pharmaceutical molecules in their different disordered forms. In this study, liquid and melt-quenched glassy carbamazepine have been studied using high energy X-ray diffraction and modeled using Empirical Potential Structure Refinement. The results show significant structural differences between the liquid and glassy states. The liquid shows a wide range of structures; from isolated molecules, to aromatic ring correlations and NH-O hydrogen bonding. Upon quenching from the liquid to the glass the number of hydrogen bonds per molecule increases by ~50% at the expense of a ~30% decrease in the close contact (non-bonded) carbon-carbon interactions between aromatic rings. During the cooling process, there is an increase in both singly and doubly hydrogen-bonded adjacent molecules. Although hydrogen-bonded dimers found in the crystalline states persist in the glassy state, the absence of a crystalline lattice also allows small, hydrogen-bonded NH-O trimers and tetramers to form. This proposed model for the structure of glassy carbamazepine is consistent with the results from vibrational spectroscopy and nuclear magnetic resonance.

Benmore, Chris J. (ORCID:0000000170077749)↗
DOE OSTI2020

(Oxy)hydroxides Formed on Aluminum Fuel Materials After Irradiation and Long-Term Wet Storage - 20354

The aluminum cladding of research-reactor fuel experiences general corrosion when in contact with water during in-reactor service and post-discharge wet storage, resulting in the formation of adherent aluminum (oxy)hydroxide films. These (oxy)hydroxides contain chemically-bound water that poses challenges for extended dry storage due to the risk of thermal or radiolytic decomposition releasing free water and/or hydrogen and oxygen gases. This study describes characterization of the (oxy)hydroxides present on several aluminum materials used in reactor operation and subsequently stored wet in the L-Basin storage facility at the Savannah River Site (SRS) for an extended period. Characterization data providing insight into the loading, composition, and morphology of (oxy)hydroxides to be expected on service-exposed aluminum cladding provides valuable benchmarks for designing adequate drying and dry-storage approaches. This work is part of a broader investigation to address knowledge gaps and technical data needs for dry storage of aluminum-clad spent nuclear fuel (ASNF), which included in-lab growth of (oxy)hydroxide films on aluminum alloy substrates to investigate formation behavior, investigation of drying methods to remove existing (oxy)hydroxides from ASNF cladding, and measurement of radiolytic yield of hydrogen from (oxy)hydroxide powders and films. In this study, (oxy)hydroxide films were characterized for three aluminum-alloy materials used in reactors and subsequently stored wet for up to approximately 40 years in L-Basin at SRS: one cropping from a Missouri University Research Reactor (MURR) fuel element (Al-6061 alloy), one cropping from a Universal Sleeve Housing (USH) (Al-6063 alloy), and one Mark-16B fuel assembly (either Al-6061 or Al- 6063). The USH and Mark-16B were used in SRS production reactors. Characterization of the as-received (oxy)hydroxides included scanning electron microscopy (SEM) in both plan-view and cross-section to characterize the (oxy)hydroxide layer's morphology, thickness, and structure. X-ray diffraction (XRD) was used to identify the chemical composition and distinguish between the various aluminum (oxy)hydroxides known to form under reactor and storage conditions. XRD analysis revealed both bayerite (Al(OH)3) and boehmite (AlOOH) on the surface of the MURR and USH samples, as well as bayerite, boehmite, and gibbsite (another Al(OH)3 polymorph) on the surface of the Mark-16B sample. The aluminum trihydroxides, bayerite and gibbsite, are typically associated with corrosion in low-temperature (<80 deg. C) water, while boehmite is expected to form at higher water temperature (>80 deg. C). The presence of bayerite on the USH, which is believed to have operated close to 90 deg. C, suggests that boehmite formed during in-reactor exposure was not protective against further hydroxide growth in low-temperature wet storage. Cross-section scanning electron microscopy (SEM) showed total (oxy)hydroxide layer thicknesses of ∼5- 10 μm for the MURR and ∼5-15 μm for the Mark-16B. The thickness of the USH's (oxy)hydroxide layer was indiscernible by the current mounting and imaging method, despite plan-view SEM and XRD confirming the presence of an (oxy)hydroxide layer. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Co‐Electrolysis of CO 2 and H 2 O to Syngas on Bimetallic Pd x Cu 1‐ x Catalysts for Tandem Thermochemical Conversion to Carbon Nanofibers

Electrification of chemical production using renewable energy and abundant feedstocks offers a promising pathway for decarbonizing the chemical industry. Current efforts on CO 2 valorization largely focus on making chemicals and fuels. Here, to help achieve net-negative emissions through long-term carbon storage, this study aims to develop efficient electrocatalysts for a tandem electrochemical-thermochemical process to convert CO 2 into carbon nanofibers (CNFs). CO 2 and water are first electrochemically reduced in a membrane electrode assembly (MEA) electrolyzer to produce syngas (CO + H 2 ), which is subsequently fed into a thermochemical packed bed reactor to facilitate CNF growth. This work systematically evaluated Pd x Cu 1-x bimetallic electrocatalysts to assess the effect of Pd–Cu alloying on enhancing syngas production while reducing Pd loading. Transmission electron microscopy and Raman spectroscopy confirmed the formation of high-purity, crystalline CNFs, regardless of the syngas composition from the MEA. In situ X-ray absorption spectroscopy and X-ray diffraction measurements revealed that increasing Cu content in the Pd x Cu 1-x alloy progressively inhibited palladium hydride formation, consistent with DFT calculations on the stability of Pd x Cu 1-x under reducing electrochemical potentials.

58 GEOSCIENCES↗
DOE OSTI2021

Nitrene Photochemistry of Manganese N ‐Haloamides**

Abstract Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of Mn III N ‐haloamide complexes. The S= 2 N ‐haloamide complexes are characterized by 1 H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N ‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate Mn II and amidyl radical intermediates; in contrast, photolysis of N ‐iodoamides proceeds via N−I cleavage to generate a Mn IV nitrenoid (i.e., {MnNR} 7 species). These results establish N ‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis.

Van Trieste, III, Gerard P.↗
DOE OSTI2024

Event generation with Sherpa 3

Sherpa is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments. We summarise new developments, essential features, and ongoing improvements within the Sherpa 3 release series. Physics improvements include higher-order electroweak corrections, simulations of photoproduction and hard diffraction at NLO QCD, heavy-flavour matching in NLO multijet merging, spin-polarised cross section calculations, and a new model of colour reconnections. In addition, the modelling of hadronisation, the underlying event and QED effects in both production and decay has been improved, and the overall event generation efficiency has been enhanced.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

On the Structural Transformation of Ni/BaH 2 During a N 2 -H 2 Chemical Looping Process for Ammonia Synthesis: A Joint In Situ Inelastic Neutron Scattering and First-Principles Simulation Study

The demand for decarbonizing the ammonia industry by using renewable energy has invoked increasing research interests into catalyst development for effective N 2 reduction under mild conditions. Hydride-based materials are among some of the emerging catalysts for ammonia synthesis at ambient pressure and low temperatures (< 673 K). A recent chemical looping process based on Ni/BaH 2 showed the most promise as it can realize ammonia production at a temperature as low as 373 K and under ambient pressure. However, the chemical transformation of the hydride catalyst at the molecular level remains unclear in this process. Here, we report detailed in situ neutron spectroscopy and diffraction investigations along with first-principles simulations on the structural transformation of Ni/BaH 2 during the nitridation and hydrogenation steps in the chemical looping process for ammonia synthesis. It was shown that a ball-milling process of the starting Ni/BaH 2 could significantly decrease the size of BaH 2 and increase the density of defects, thus potentially enhancing the reactivity of the hydride. The evolution from BaH 2 to barium imide (BaNH) was evidenced in the inelastic neutron scattering (INS) and neutron diffraction results during the N 2 reaction step. During the hydrogenation study, in addition to the recovery of BaH 2 , a possible intermediate species, N-deficient barium imide, was also detected. In comparing the N 2 and H 2 reaction steps, the neutron results indicate that the hydrogenation step appears more difficult than the nitridation step, confirming the facile N 2 fixation property of Ni/BaH 2 catalyst in ammonia synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Optical vibrational spectra and proposed crystal structure of ε-UO 3

ε-UO 3 is an exotic polymorph in the uranium trioxide system with an undetermined crystal structure and limited optical vibrational spectroscopic data. To improve understanding of this compound, we synthesize and investigate the crystal structure and optical vibrational spectra of ε-UO 3 . Infrared spectra collected for ε-UO 3 are in good agreement with previously published results, and our studies extend the available data into the low-energy (600–100 cm –1 ) regime. For the first time, Raman spectra are presented for ε-UO 3 using both 785 and 532 nm excitation wavelengths. Previous reports suggest an impurity phase may be present in ε-UO 3 produced by calcination of U 3 O 8 ; however, spectral center-of-mass calculations, principal component analyses, and Raman spectroscopic mapping employed to investigate this possibility indicate that the product of U 3 O 8 calcined in O 3 (g) in this work is likely phase-pure. A possible novel structure solution for ε-UO 3 is determined via Rietveld refinement of powder X-ray diffraction data and is triclinic, P-1, with a = 4.01 Å, b = 3.85 Å, c = 4.18 Å, and α = 98.26°, β = 90.41°, γ = 120.46° (R wp = 8.30%). The asymmetric unit of ε-UO 3 consists of U(VI) in hexagonal bipyramidal coordination with displaced equatorial oxygen. Further analysis reveals that the structure of ε-UO3 is best described by a 2 × 1 × 2 supercell structure in P-1 with a = 8.03 Å, b = 3.86 Å, c = 8.37 Å with α = 98.26°, β = 90.41°, and γ = 120.46°, although a higher-symmetry structure is possible. Optical vibrational spectroscopic and structural measurements of ε-UO 3 presented here furthers our understanding of this complex uranium oxide and clarifies the origin of reported structural similarity to U 3 O 8 .

-UO3↗
DOE OSTI2024

Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H 2 O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors’ adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Accelerator physics at NSLS-II: research accomplishments in 2020

NSLS-II accelerator physicists provide scientific support for user operations, as well as for improvements and developments of the accelerator systems. This work includes optimization of the NSLS-II performance with high beam current and low vertical emittance, improvement of the beam stability, development of new software tools for operations and beam studies. The accelerator physicists productively worked on a number of research activities such as the conceptual design of NSLS-II accelerator upgrade; design and optimization of advanced low-emittance lattices; development of novel methods to study nonlinear beam dynamics; ultrafast electron diffraction and microscopy. The physicists also contributed to the BNL electron-ion collider project, to the APS and ALS upgrade projects. Research accomplishments achieved in 2020, are summarized in this report.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

In situ probing of interfacial roughness and transient phases during ceramic cold sintering process

The ceramic cold sintering process (CSP) offers an eco-friendly approach to producing fully dense ceramics at low temperatures. However, an incomplete mechanistic understanding hinders its optimization and widespread adoption. In this study, we analyze the microstructural and structural changes in ZnO, a model CSP system, using in situ synchrotron-based high-energy small-angle X-ray scattering and X-ray diffraction techniques. Our results reveal the time evolution of ZnO particles' surface area and roughness, reflecting the dissolution and re precipitation processes that enable densification. The in situ measurements supply valuable kinetic data for these stages of CSP. Alongside microstructural changes and densification, we observed the evolution of secondary phases representing reaction products between ZnO and acetic acid, the solvent used. The initial ZnO/solvent mixture's dominant secondary phase is attributed to zinc acetate, which is gradually replaced by a zinc soap-type structure during CSP. This structure has a large (≈ 21 Å) lattice parameter and is assumed to have a layered nature. The formation of this soap phase, which is retained in the sintered product as an intergranular component, appears to be a signature of successful cold sintering as it facilitates mass transport, leading to densification. Here, our study underscores the potential of in situ synchrotron characterization for revealing microstructural and phase-evolution details during CSP. These findings, which would be challenging to obtain through ex situ measurements, provide crucial data to guide and validate theoretical models, ultimately enhancing CSP's effectiveness and adoption.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Adsorption of Iodine on Metal Coupons in Humid and Dry Environments

In this study, five different metal coupons were evaluated for gaseous iodine [I2(g)] adsorption including two stainless steels (i.e., SS304 and SS316), two Inconel® alloys (i.e., 625 and 718) and pure Ni (i.e., Ni-200) within a dynamic flow-through system where temperature, iodine concentration, flow rate, atmosphere, and relative humidity were controlled. Humidity was shown to be critical to iodine adsorption on SS304 and SS316 and Ni-200 at ambient temperatures. The results presented herein suggest that a moisture mediated reaction is occurring. However, higher humidity levels decrease the adsorption, suggesting an ideal range of humidity for highest corrosion. A comparison of the five metal substrates showed the highest I2(g) adsorption in the following descending order Ni-200 > SS304 > SS316 >718>625.The 625 and 718 Inconel alloys were fairly inert to iodine adsorption under the conditions tested. Characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction of the Ni-200 coupon indicates that NiI2 is formed and flakes off the surface as a black powder. The SS304 and SS316 coupons showed evidence of extensive reactions with I2(g) and formed a much more deliquescent corrosion product, which reacted with air when removed from the flow-through system for weighing on the analytical balance. These findings assist in predicting iodine adsorption behavior on a variety of metal surfaces under various conditions.

Beck, Chelsie L.↗
DOE OSTI2024

Enhanced Methanol Synthesis from CO 2 Hydrogenation Achieved by Tuning the Cu–ZnO Interaction in ZnO/Cu 2 O Nanocube Catalysts Supported on ZrO 2 and SiO 2

The nature of the Cu–Zn interaction and especially the role of Zn in Cu/ZnO catalysts used for methanol synthesis from CO 2 hydrogenation are still debated. Migration of Zn onto the Cu surface during reaction results in a Cu–ZnO interface, which is crucial for the catalytic activity. However, whether a Cu–Zn alloy or a Cu–ZnO structure is formed and the transformation of this interface under working conditions demand further investigation. Here, ZnO/Cu 2 O core–shell cubic nanoparticles with various ZnO shell thicknesses, supported on SiO 2 or ZrO 2 were prepared to create an intimate contact between Cu and ZnO. The evolution of the catalyst’s structure and composition during and after the CO 2 hydrogenation reaction were investigated by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct effect on the oxidation state of Zn, which, in turn, affects the catalytic performance. High Zn loadings, resulting in a stable ZnO catalyst shell, lead to increased methanol production when compared to Zn-free particles. Low Zn loadings, in contrast, leading to the presence of metallic Zn species during reaction, showed no significant improvement over the bare Cu particles. Therefore, our work highlights that there is a minimum content of Zn (or optimum ZnO shell thickness) needed to activate the Cu catalyst. Furthermore, in order to minimize catalyst deactivation, the Zn species must be present as ZnO x and not metallic Zn or Cu–Zn alloy, which is undesirably formed during the reaction when the precatalyst ZnO overlayer is too thin.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Probing the hydrolytic degradation of UF 4 in humid air

This manuscript describes the chemical transformations that occur during hydrolysis of uranium tetrafluoride (UF 4 ) due to its storage in humid air (85% and 50% relative humidity) at ambient temperatures. This hydrolysis was previously reported to proceed slowly or not at all (depending on the percent relative humidity); however, previous reports relied primarily on X-ray diffraction methods to probe uranium speciation. Here, we employ a battery of physiochemical probing techniques to explore potential hydrolysis, including Raman spectroscopy, powder X-ray diffraction, 19 F nuclear magnetic resonance spectroscopy, scanning electron microscopy, and focused ion beam microscopy with energy-dispersive X-ray spectroscopy. Of these, only Raman spectroscopy proved to be particularly useful at observing chemical changes to UF 4 . It was found that anhydrous UF 4 slightly oxidizes over the course of thirteen days to Schoepite-like uranium complexes and possibly UO 3 . In contrast, UF 4 exposed to 50% relative humidity slightly decomposes into UO 2 F 2 , Schoepite-like uranium complexes, and possibly a high order uranium oxide that eluded chemical assignment (U x O y ). Despite the rich chemical speciation observed in our Raman spectroscopy measurements, X-ray diffraction and 19 F NMR measurements on the same material showed no changes. Microscopy measurements suggest that the observed reactions between UF 4 and water occur primarily on the surface of UF 4 particulates via a method that is visually similar to surface corrosion of metals. Therefore, we postulate that NMR spectroscopy and X-ray diffraction, which are well-suited for bulk analysis, are less suited than Raman spectroscopy to observe the surface-based reactions that occur to UF 4 when exposed to humid air. Considering the importance of UF 4 in the production of nuclear fuel and weapons, the results presented herein are widely applicable to numerous nuclear science fields where uranium detection and speciation in humid environments is of value, including nuclear nonproliferation and nuclear forensics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Acid-catalyzed C–H reductive elimination from Au (III)

An unusual mode of C–H reductive elimination from a Au III complex catalyzed by acid is reported. The addition of triflic acid (HOTf) to [( tBu PCP)Au III –H]OTf (1-OTf, tBu PCP = 2,6-C 6 H 3 (CH 2 P t Bu 2 ) 2 promotes formal C–H reductive elimination. The Au I product [( tBu P(C–H)P)Au I ]OTf (2-OTf, tBu P(C–H)P = κ 2 (1,3-C 6 H 4 (CH 2 P t Bu 2 ) 2 )) was characterized by NMR spectroscopy and X-ray diffraction. It was shown that the reductive elimination of 1-OTf has a dependence on the identity of the acid catalyst which cannot be explained by acid strength. Mechanistic experiments are consistent with a concerted mechanism for C–H reductive elimination involving participation of basic moieties on the acid.

Ardon, Yotam [University of Pennsylvania, Philadel↗